Normal variation in, and effect of 2% pilocarpine on, intraocular pressure and pupil size in female horses

Abstract

Objective - To determine normal variation in, and effect of 2% pilocarpine hydrochloride on, intraocular pressure (IOP) and pupil size in female horses during a specified period. Animals - 10 female horses with normotensive eyes. Procedure - IOP and horizontal and vertical pupil size were measured on a single day between 8 AM and 8 PM at hours 0, 0.5, 1, 2, 4, 6, 8, 10, and 12. Measurements were repeated after single- dose application of 2% pilocarpine to both eyes. IOP and pupil size were measured at 8 AM and noon in a 5-day experiment of twice-daily application of 2% pilocarpine. Results - Variation in IOP and pupil size was not significant between 8 AM and 8 PM. Change in IOP or pupil size after a single dose of 2% pilocarpine also was not significant. In the multiple-dose experiment, the IOP at noon on the fifth day was significantly higher than the IOP in the morning on the first and second days. The IOP in the morning on the fifth day was significantly higher than the IOP in the morning and at noon on the first and second days. The IOP at noon on the fourth day was significantly higher than the morning IOP on the first and second days and at noon on the first day. The decrease in vertical pupil size was significant. Conclusions - Between 8 AM and 8 PM variation in IOP and pupil size in normotensive eyes of horses is not significant. Two percent pilocarpine dose not significantly change IOP between 8 AM and 8 PM in clinically normal horses after a single dose or multiple twice-daily applications. After multiple twice-daily applications, a trend toward an increase in IOP was seen, and the decrease in vertical pupil size was significant.